Dodecahyrdo-3a,6,6,9a-tetramethylnaphtho[2,1-b]furan (1) is an important fragrance chemical (see U.S. Pat. No. 3,029,255). It has been used in high quality perfume compositions and in functional products, such as fragrances for toiletries and household products, where a persistent amber effect is desired. Compound 1 is also a component of tincture of ambergris [see B. D. Mookherjee and R. R. Patel, Proceedings of the 7th International Congress of Essential Oils, Kyoto, Japan, (1977), paper number 136], and synthetic 1 has been used in artificial ambergris formulations. Compound 1 may be manufactured from 2-ethenyldecahydro-2-hydroxy-.alpha.-2,5,5,8a-pentamethyl-1-naphthalenepro panol (4), commonly referred to as Sclareol, obtained from Clary Sage (Salvia Sclarea).
U.S. Pat. No. 3,050,532 discloses a method of converting Compound 4 into dodecahydro-3a,6,6,9a-tetramethylnaphth[2,1-b]furan-2(1H)-one (2) using a two-stage oxidation sequence. In the first step an aqueous dispersion of Sclareol is intimately contacted with an alkali metal permanganate oxidizing agent, under alkaline conditions, to partially oxidize the Sclareol. During the second step the resulting aqueous reaction mixture from the first step is acidified and intimately contacted with a permanaganate or chromic acid oxidizing agent under acid conditions, thereby completing the oxidation.
Compound 2 may be readily converted to Compound 1 by known methods. For example, reducing Compound 2 with hydride reagents (see for example, Helv. Chim. Acta 1950, 33, 1308) provides decahydro-2-hydroxy-2,5,5,8a-tetramethylnaphthaleneethanol (3) which is readily converted by cyclization to Compound 1.
U.S. Pat. No. 3,029,255 discloses a method for making Compound 1 by dehydrating Compound 3 with Al.sub.2 O.sub.3 at 200.degree.-225.degree. C., followed by heating in vacuo in the presence of .beta.-naphthalene sulfonic acid (130.degree. C. up to 160.degree. C.) to effect cyclization to Compound 1.
Alternatively, Compound 1 may be obtained by cyclization of Compound 3 using toluene-p-sulfonyl chloride in pyridine, as disclosed by Cambie et al. (see Aust. J. Chem., 1971, 24, 591).
There is no teaching or suggestion in the prior art of converting labdane compounds via microbiological methods into decahydro-2-hydroxy-.alpha.,2,5,5,8a-tetramethylnaphthaleneethanol (3) or dodecahydro-3a,6,6,9a-tetramethylnaphtho[2,1-b]furan (1), according to the novel and commercially efficient process provided by this invention.